The efficiency of a cooling or heating system can be described by the Coefficient of Performance, which is the ratio of the change in heat compared to the amount of supplied work. A conventional household air conditioner has a coefficient of performance typically in the range of 1.0 to 3.0. A conventional household furnace has a coefficient of performance close to 1.0, while systems utilizing conventional geothermal technology are typically in the range of 3.5 to 5.0.
Geothermal heating and cooling systems transfer the warmth or cold from the ground below to the home or building above. The earth is a natural heat source or sink, with year-round temperatures of fifty-five to seventy degrees Fahrenheit just below the surface. When the system is in cooling mode, the earth (heat sink) absorbs the heat of the working fluid, and when the system is in heating mode the working fluid absorbs the heat of the earth (heat source).